Semiconductor memories are used in many electronic systems to store data that may be retrieved at a later time. As the demand has increased for electronic systems to be faster, smaller, have greater computing ability, and consume less power, semiconductor memories that may be accessed faster, are compact, store more data, and use less power have been continually developed to meet the changing needs. Part of the development includes creating new specifications for controlling and accessing semiconductor memories, with the changes in the specifications from one generation to the next directed to improving performance of the memories in the electronic systems.
Semiconductor memories are generally controlled by providing the memories with command signals, address signals, clock signals. The various signals may be provided by a memory controller, for example. The command signals may control the semiconductor memories to perform various memory operations, for example, a read operation to retrieve data from a memory, and a write operation to store data to the memory. With newly developed memories, the memories may be provided with system clock signals that are used for timing command signals and address signals, for example, and further provided with data clock signals that are used for timing read data provided by the memory and for timing write data provided to the memory.
With regards to memory designs using data clock signals, the data clock signals are provided to a memory (e.g., from a memory controller) to synchronize provision of read data or receipt of write data by the memory. The data clock signals are provided according to a specification with a timing relative to receipt of a memory command in order to provide data or receive data to satisfy a specified timing. The memory responds to the active data clock signals and provides or receives the data accordingly.
Clock circuits included in a semiconductor memory may be used to generate internal clock signals that are used for performing various operations. For example, some clock circuits may provide multiphase clock signals based on the data clock signals. The multiphase clock signals may be used, for example, for timing the provision and/or receipt of data by the memory. The multiphase clock signals have relative phases with one another (e.g., 90 degrees) and with the data clock signals. In some memories, the clock circuits provide the multiphase clock signals having a phase relationship relative to the data clock signals that is unknown until determined by evaluation of one or more of the multiphase clock signals.
Conventional clock circuits for generating internal clock signals, however, are often cumbersome, including several complex circuits, and may have a relatively long path delay between receiving input clock signals and providing output clock signals due to having several complex circuits coupled between the input and output. Additionally, conventional clock circuits may have a relatively long recovery time from when input clock signals begin clocking from common clock levels.